Since prostaglandin (hereinafter referred to as "PG") exhibits various important physiological actions in a trace amount, the syntheses of the derivatives from natural PGs and the biological activities have been investigated with the intention of a practical use as medicines and have been reported in many literatures.
Particularly, PGs have been reported on their various central nervous actions and have been clarified as to the intracerebral content, biosynthesis, metabolic pathway, their intracerebral localizations and changes with growth or aging, and there has been taken an interest in the relation of PGs with sleep and wake. Among them, PGD.sub.2 has been known as an intracerebral humoral factor which controls the occurrence or maintenance of sleep, and it was made clear that the sleep induced by PGD.sub.2 in monkeys is undistinguished from the spontaneous natural sleep in brain wave or behavior (Proc. Natl. Acad. Sci. USA, vol. 85, pp. 4082-4086 (1988)), therefore this compound was expected as a compound having a novel sleep-inducing action.
However, PGD.sub.2 derivatives including PGD.sub.2 are presently unpractical due to the problems concerning the effect and the stability as a drug.